The present invention relates to a method for reporting network status, in a communications network, to a data source with an adaptive transmission rate in order to enable said data source to adapt said transmission rate based on said network status, said communications network further containing at least one intermediate network node and a data sink, and also relates to a communications network comprising at least one data source with an adaptive transmission rate, at least one intermediate node and at least one data sink, with the data source being able to adapt the transmission rate on the basis of network status information.
Such a method and communications network are already known in the art, e.g. from the section Flow Control Model and Service Model for the ABR Service Category, pages 7-11 in “Traffic Management Specification Version 4.0” from the author Natalie Giroux published in April 1996 by the ATM Forum (ATMF) Technical Committee.
Therein, the Available Bit Rate flow control is described. This Available Bit Rate flow control occurs between a data source, called a sending end-system and a data sink, called a receiving end-system. A data source and a data sink are connected via bi-directional connections over a communication network containing a number of intermediate network nodes, called network elements. In this Available Bit Rate flow control method, the intermediate network nodes and the data sink report to the data source on congestion in the communications network.
A source generates forward RM-cells, which are turned back by the data sink and sent back to the source as backward RM-cells. These backward RM-cells carry feedback information provided by the intermediate network nodes and the data sink, to the data source. An intermediate network node directly inserts feedback control information into RM-cells when they pass in the forward or backward direction and indirectly informs the data source about congestion. The data sink will update this congestion information in RM-cells, and generate backward RM-cells. The data source then adapts its traffic in accordance with the feedback in order to get a low cell loss ratio. Determination and reporting of network congestion by each of the intermediate network nodes together with the data sink in this flow control method, leads to a very complex approach. At present the stability of this approach is not proven. Moreover, the complexity it introduces into the network is considerable. Besides, it is not possible to support this mechanism in a heterogeneous network hosting different transport technologies such as Asynchronous Transfer Mode and Frame Relay as it requires all the nodes involved, to support the ABR mechanism.